A power supply controller can be used as a so-called high side driver, which has an n-channel MOSFET inserted between a positive power source and a load to perform current control, as described in Japanese Patent Laid-Open No. 2001-217696, for example. When a power supply controller is used as a high side driver in such a manner, the gate voltage of the MOSFET must be driven to a level higher than a power supply voltage (typically to a voltage approximately twice the power supply voltage) for the MOSFET to reliably turn on. For this purpose, a gate driving circuit (for example a charge pump circuit) is required. In particular, a gate driving circuit receives a predetermined input voltage. When an ON signal for turning on the MOSFET is input from an external source to the power supply controller, the gate driving circuit rises the input voltage and outputs the risen voltage to the gate of the MOSFET to turn on the MOSFET.
The gate driving circuit controls the gate electric potential of the MOSFET on the basis of the electric potential at a ground terminal provided in the power supply controller to turn off the MOSFET. Accordingly, when the ground terminal is not grounded and the source of the MOSFET is properly grounded through a load, the electric potential at the ground terminal approaches the electric potential of the positive power source and, along with this increase, the gate electric potential of the MOSFET also increases and approaches the electric potential of the positive power source. As a result, regardless of input of the ON signal the potential difference between the source and gate (the gate-source voltage) of the MOSFET exceeds a threshold voltage of the MOSFET and can erroneously cause the MOSFET to turn on.